Ingredient guide
Bladderwrack is a brown seaweed sold for thyroid support and weight, mostly via its iodine content. Modern human evidence is sparse. Heavy metal contamination and very high iodine are real safety concerns with this product category.
Limited evidenceBladderwrack is a leathery brown seaweed (Fucus vesiculosus) common along North Atlantic and Pacific coasts. The air-filled bladders that give it its name help it float. It has been used in folk medicine for thyroid problems, mostly for its high iodine content, and is also sold for weight.
Modern human evidence is sparse. There is laboratory work supporting antioxidant and anti-inflammatory activity from fucoidan and other compounds, but it has not translated into clear clinical benefits at scale. The real-world concerns are contamination with heavy metals and unpredictably high iodine. We grade the evidence as limited and the safety case as more important than the benefit case.
Trials and traditional use range widely. About 500 mg of extract per day is the most cited bioactive dose, but there is no established standard. Ask your healthcare provider before use, especially if you have a thyroid condition or take thyroid medicine.
Not necessarily. Its iodine content is high and variable, which can disrupt thyroid hormone levels. Anyone with a thyroid condition should ask a doctor first.
Yes. Seaweed can accumulate arsenic, cadmium, and lead from sea water. Choose products tested and certified for low contamination.
